K. Mutwil

Numerical Modeling as the Method to Determine the Parameters of Tube Bending with Local Induction Heating

The numerical analysis results of bending with local induction heating of 10CrMo9-10 steel tubes have been presented in the paper. The goal of conducted simulations was to determine the process parameters that allow to obtain tube bends with geometric features which meet requirements of relevant standards. The risks of wrinkling, excessive tube bend ovalization and cracking (according to Cockroft-Latham criterion) have been analysed. The obtained results prove that numerical modeling can be used to minimize the costs of tube bending technology implementation without the need of further process parameters corrections.

GEOMETRICAL PHENOMENA IN TUBE BENDING WITH LOCAL INDUCTION HEATING

A theoretical and experimental analysis of heat induction bending for tubes used in the power industry is performed. First, the design of the heat induction bending process for tubes is described and industrial application areas for this technology are presented. Next, the main methods for tube bending with local induction heating are discussed and the effect of the technology on geometrical parameters of bends formed is presented. Then, the heat induction bending process for tubes is modeled using numerical techniques (FEM). The simulations are performed in a three-dimensional strain state, where thermal phenomena are taken into account, using the commercial software package Simufact Forming v. 11.0. In the simulations, the changes in workpiece geometry in the region of the bend being made (cross section ovalization, darkening and thickening of walls, neutral axis position) are examined. Also, potential phenomena that could limit the stability of the bending process and cause shape defects are predicted. The results of the numerical modeling are then compared to those obtained under industrial conditions.

Study on Cracking Process of Power Boiler Element

This paper presents the study of the reasons for cracking of spray steam attemperator. The element being analysed is a temperature controller of steam for turbine; its proper functioning has considerable impact on operation of power generating set of boiler and turbine. Damage to the steam attemperator may affect the durability of neighbouring components, replacement or repair of which results in a long-term outage of power generation unit. The reason for attemperator cracking has been determined on the basis of strength calculations and micro-and macro-analysis of fracture surfaces. The conducted tests were the basis for modification of attemperator design, which will ensure reliable functioning of the analysed element.

Low cycle fatigue life and creep life of material in tube bends made of 15NiCuMoNb5-6-4 steel

The article addresses results of tests of performance characteristics of a tube bend made of the 15NiCuMoNb5-6-4 steel, the latter being for manufacture of feed water pipelines used in power engineering systems. The tube bend was developed by bending with local induction heating, and the optimum tube bending parameters were established based on numerical simulations of the bending process. The mechanical properties of the tube bend were attained through quenching and tempering. Tests of mechanical properties were conducted using samples collected at different zones of the tube bend (the straight one as well as those subject to tension and compression), and compared with properties of the as-delivered tube material. The established basic mechanical properties of the tube bend, required under the applicable standards, were supplemented with results of low-cycle fatigue and creep tests, the purpose of which was to acquire information on the tube bend material service life under conditions of steady and unste...

Analysis of the Cracking Processes of Jointing Components Used in Turbine Valve Chest

Root causes of premature breakage of the bolts fastening the connection members of shut-off valves in valve chests for secondary superheated steam. The experiments showed that the cracking of bolts had been caused by the process of accelerated creeping under high tensile stresses. The obtained results may constitute the basis for formulation of operating guidelines and recommendations, resulting in extended life of the components under consideration.

Fatigue Cracking Processes of a Thick-Walled Component of a Chemical Pipeline

At present, there are no generally accepted and widely recognized procedures to determine condition of material of devices subject to complex long-term thermo-mechanical loads. Condition of pipeline material usually changes when subjected to the conditions of long-term operation. Its structure changes and, consequently, so do its mechanical properties, including fatigue characteristics and crack resistance. Therefore, the durability of a component operating under thermal and mechanical loads cannot be discussed separately from its current material properties. This applies in particular to changes that take place in the material micro-structure and to their connection with mechanical properties. This paper covers analyses of stress in the material of a selected pipeline component – pipe tee that is used in chemical plants. Thermo-mechanical interactions determining stress distribution in the component have been taken into account in the calculations. Morphology and location of the cracks indicated that a fatigue-like nature of impacts was the cause of material destruction. Loads of this type occur mainly in conditions of start-up and shut-down. For these reasons, condition of the material in the above-mentioned unstable conditions was subjected to numerical stress analysis. Due to geometric complexity of the pipeline, the distribution of stress in the T-pipe was calculated in two stages: the object was modeled from a global and local perspective. The resulting stress distributions helped to determine factors affecting durability of the tested object. Metallurgy tests were also conducted in order to ascertain factors determining the degradation of material structure and processes of crack formation and development. As a result of research one ascertained that the process of T-pipe cracking under operating conditions was a combined effect of thermo-mechanical and chemical actions determined by the course of intercrystalline corrosion. Synergic interaction of corrosion processes and variable thermal and mechanical loads caused nucleation and propagation of cracks. The crack systems in T-pipe areas subject to the highest stress showed courses characteristic for thermal fatigue of material. The results obtained will identify degradation mechanism of materials used in chemical installations.